Ferraris sensor

The Ferraris sensor (also known as Ferraris acceleration sensor or relative acceleration sensor ) is an acceleration sensor that measures the relative acceleration of two components without contact using the eddy current principle discovered by Galileo Ferraris . It was developed by Lothar Wilhelmy as a rotary acceleration sensor for drive technology and, together with Bernhard Hiller, adapted to different measuring tasks. The Ferraris sensor does not have a spring-mass system like other acceleration sensors and is therefore independent of centrifugal and gravitational acceleration .

The Ferraris sensor is used on test benches for system analysis, investigation of torsional vibrations and is used to improve the control of highly dynamic servo drives in printing machines, linear drives and robots.

functionality

Scheme of a Ferraris sensor, the distance between the magnet (green) and the eddy current plate (gray) has been increased.

The moving component contains a non-magnetic, electrically conductive body, the change in speed of which is to be measured. In the case of rotational acceleration measurement, this is a disk, in the case of linear acceleration measurement, a sheet metal strip made of aluminum or copper.

A permanent magnet generates a temporally constant, spatially limited magnetic field perpendicular to the direction of movement. This creates eddy currents i in the moving body. These eddy currents cause secondary magnetic fields (dashed in the picture), the strength of which increases with speed. This change induces a voltage in the pickup coil. Since this coil only detects the changes in the magnetic field, the induced voltage u is proportional to the acceleration . ${\ displaystyle {\ dot {v}}}$

{\ displaystyle u \ sim {\ dot {v}}}

advantages

The sensor measures the relative acceleration. This makes it interesting for use in multi-axis robots and machine tools, where otherwise the acceleration due to gravity has to be taken into account in calculations.

It has a high linearity and a high signal-to-noise ratio .

In digital servo drives, the direct measurement of the acceleration can be used as a feedback signal (e.g. for system damping) or to set up a subordinate acceleration control that enables a significant increase in the rigidity and dynamics. In addition, a low quantized speed can be calculated through integration.

disadvantage

The disadvantage is power loss, which, like eddy current brakes, heats the disk or sheet metal. As the speed increases, the sensor also loses its sensitivity .

Individual evidence

↑ DE 198 28 372 C2, patent granted on August 31, 2000
↑ DE 101 18 954 C1, patent granted November 14, 2002
↑ EP 1 377 838 B1, patent granted February 1, 2006
↑ EP 1 597 594 B1, patent granted September 13, 2006
↑ Dipl.-Ing. Bernhard Hiller "New developments and applications of the Ferraris sensor" in the seminar: Advances in control and drive technology, Stuttgart, ISW, 2005 pdf 3.5 MByte

[1] DE 198 28 372 C2, patent granted on August 31, 2000

[2] DE 101 18 954 C1, patent granted November 14, 2002

[3] EP 1 377 838 B1, patent granted February 1, 2006

[4] EP 1 597 594 B1, patent granted September 13, 2006

[5] Dipl.-Ing. Bernhard Hiller "New developments and applications of the Ferraris sensor" in the seminar: Advances in control and drive technology, Stuttgart, ISW, 2005 pdf 3.5 MByte